1. Field of the Invention
The invention relates to computer systems which boot from various media, and more particularly to a computer system which can boot from alternate SCSI media such as CD-ROM and tape drives, particularly when the operating system is MS-DOS.
2. Description of the Related Art
It has been conventional for personal computers to boot from various media, for example a floppy disk drive or a hard disk drive. In certain cases personal computers can also boot from external locations, such as over a network or over parallel or serial ports. Generally, the order of trying the various sources is a fixed arrangement, such as the external boot location, the floppy drive and finally the first hard drive. In certain cases, bypassing of the floppy drive has been provided to allow certain security features.
One trend in the personal computer field is the ever increasing size of programs, including diagnostic programs, configuration programs and application programs. The diagnostic programs are getting longer because they must generally handle a very large number of systems, as new systems are developed, and because the systems are getting significantly more complex. As to configuration, with the development of programs such as EISA CONFIG, which is a configuration utility used for EISA computers, it is also standard to include a very large number of standard board setup or configuration files. As time passes, the number of files with the utility continues to increase, so that the user need not necessarily find the actual floppy disk that came with the circuit board, but can just consult the table provided with the utility. So as more boards are produced, the number of configuration files continues to increase, easily exceeding the capacity of a single floppy disk drive.
The third problem is the ever growing size of operating system and application programs. As the computers have become more powerful and better user interfaces and additional functionality have been demanded, the program sizes have dramatically increased. In many cases 10 to 20 1.44 MB floppy diskettes are required to contain the copy of the program to be loaded onto the computer's hard disk for use thereafter. And the program files on these diskettes have already been compressed.
All of these trends have resulted in a need for a growing number of floppy disks which are quite cumbersome, expensive, bulky and subject to accidental erasure. Therefore some avenue is considered desirable to greatly reduce the logistical difficulties of a user running diagnostics or configuration programs or installing applications or operating systems.
The first thought that would immediately come to mind would be the use of CD-ROMs to contain these programs. To this end, the International Standards Organization (ISO) has developed standards for data on CD-ROMs. This includes an area reserved for the manufacturer; a primary volume descriptor, which is a block which indicates the size of the actual data stored on the CD-ROM drive; an ISO defined boot record; several ISO defined volume partition descriptors; and a volume descriptor terminator. The volume descriptor terminator is followed by the primary volume space, which includes any volume partitions, such as the main volume, and any additional volumes, such as a 1.44 MB floppy image and a 1.2 MB floppy image. While this would appear to solve the problem, it does not. The reason is that there is no manufacturing support for preparing a bootable ISO CD-ROM and there is no software which recognizes an ISO-standard bootable CD-ROM. Systems are not available to write data to the various locations specified by the ISO for the boot record, the various volume partition descriptors, and the volume descriptor terminator. Available systems can only write to the system area, the primary volume descriptor and the primary volume space. As a result, while there is a specification, it is not possible to actually develop a CD-ROM which is bootable according to the ISO standard. A second problem is that any additional devices are not in the boot order in a standard computer. It is also desirable to limit any changes made to incorporate booting from a CD-ROM drive so that the various conventional routines, commonly BIOS interrupts, which are utilized in the computer do not need to be redefined but can continue to remain compatible with present functions while being extended for new capabilities. It is also desirable that several variations of CD-ROM organizations be capable of being utilized for booting.